What is DeltaH_f^@ for NO(g)?

1 Answer
anor277
Nov 20, 2016

For "NO", DeltaH_f""^@=+91.3*kJ*mol^-1; and thus here DeltaH_f""^@-=DeltaH_"rxn"^@

Explanation:

To account for the positive value, consider what DeltaH_f""^@ represents:

" the enthalpy associated with the formation of 1 mole of substance from its constituent elements in their standard states under given conditions....... "

So here, DeltaH_f""^@ is the enthalpy associated with the following reaction:

1/2N_2(g) + 1/2O_2(g) rarr NO(g) ;DeltaH""^@""_"rxn"=91.3*kJ*mol^-1

In order to make the N=O bond, we have to break exceptionally strong N-=N and O=O bonds. The energy shortfall is anticipated.

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